This invention relates, in general, to devices for indicating the amount of liquid in a container, or the like, and, more particularly, to such devices which provide such information by use of a remote indicator.
There are many devices for indicating the level of liquid in a container. The most common is the common dipstick inserted into the crankcase of an automobile. This measurement is made directly and is messy and inconvenient.
There have been a number of devices suggested for making remote measurements of the level of oil in an automobile. One basic class of devices uses a float. As the float is buoyed up by the oil in the crankcase, means are provided to remotely provide an indication of the oil level. The oil level is used as a measurement of the amount of oil in the crankcase. Such devices have been proposed by Vincent in U.S. Pat. No. 4,034,608, Van Scoy et al. in U.S. Pat. No. 2,671,893, and Kress in U.S. Pat. No. 3,953,845.
The disadvantage of float devices is that they are responsive to the angle that the oil assumes in the crankcase. Oil level is, in turn, dependent upon the orientation of the vehicle. Thus, an indication of "low" oil may in fact be a reflection of the position of the vehicle. False indications are possible.
An alternative device has been suggested by Raby in U.S. Pat. No. 2,588,761. Raby provides an oil level indicator in which the dipstick is replaced by a hollow tube of which one end is in the crankcase and the other end communicates with a float chamber. In the float chamber is a float. The float chamber is, in turn, connected to a second hollow tube. This second hollow tube communicates with a valve. The other side of the valve communicates with a vacuum source. A push-button is mechanically linked to the valve. When the push-button is depressed, the vacuum source is connected to the second tube. The vacuum thereupon draws oil up the tube from the crankcase and into the float chamber. The float in the float chamber is mechanically linked to a diaphragm. If sufficient oil is drawn into the float chamber, the float will rise up moving the diaphragm. The diaphragm is connected to an electrical switch. The distortion of the diaphragm causes the closing of the switch and the subsequent lighting of a light indicating sufficient oil. If there is sufficient oil in the float chamber to cause the distortion of the diaphragm a second light remains on indicating that there is an insufficient amount of oil. The device proposed by Raby is extremely complex involving the use of suction, float, diaphragm, and interrelated electrical contacts. Raby also proposes the use of an intricate valve system and an external vacuum system. Furthermore, measurement is made by the transfer of oil from the crankcase to a second chamber, all of which makes for an exceedingly complicated device with various points of obvious weakness. The drawing of oil to fill a float chamber also is a disadvantage. Such a system mandates a strong suction. This is particularly true when one considers the wide changes of temperature to which an automobile is subject. The changes in temperature have a direct effect on the viscosity of the oil, thereby requiring an extremely strong vacuum for the system to work under all conditions.
Still another device has been proposed by Sherman, in U.S. Pat. No. 2,717,991. In Sherman, a hollow dipstick is connected to a piston slidably moveable within a solenoid coil. When electrical energy is applied to the solenoid coil, the generated magnetic field causes the piston to move upwardly. At the upper end of the solenoid are a pair of opposed contacts which are normally closed. The contacts are spaced over the axis of the solenoid coil. If air is drawn into the dipstick, the piston moves upwardly, and the contacts are separated. The opening of the contacts causes a break in the current flow to the solenoid. The magnetic field collapses and the piston drops. As soon as the piston drops, the contacts close again causing the solenoid to be activated and the piston to rise sharply again. A light bulb is in series with the solenoid circuit. As a result, the alternating on and off of the solenoid causes a blinking of the light bulb to thereby indicate remotely to the user that the oil in the crankcase of the vehicle is low.
If, instead of air, oil is drawn into the dipstick, the piston will rise slowly. The contacts will remain closed for longer periods of time. The more slowly blinking light bulb is intended to indicate that there is a sufficient quantity of oil.
There are many disadvantages to this device. Sherman measures the rate of flow of the oil into the hollow dipstick. Obviously, there is significant variation in oil viscosity in hot climates as opposed to colder areas. Under conditions of great engine heat or high ambient temperatures, the piston will move much more quickly than in colder climates. This may provide a false indication or lead to an accidental misreading of the blinking light. If the hole in the dipstick is somehow restricted by a partial clogging of the metering hole, a false indication may be given. Still another significant disadvantage is the potential for explosion. Thus, it should be observed that the piston of the Sherman device separates the contacts in the atmosphere of oil vapors. Such separation is likely to cause a spark. Oil fumes, which are obviously highly flammable, may be in the container formed about the Sherman device. Sherman places the bulb across the contacts and employs that as an arc suppressor. However, suppression of an arc may not eliminate a spark at the contacts. Such a spark may ignite the oil fumes. A further disadvantage to the Sherman device are the number of variables which determine the accuracy of the indicator. The operation of the device is dependent upon the inertia of the piston, friction between the piston and solenoid coil, changes in the magnetic field (as the field is alternately generated and collapsed), moisture, condensed oil vapors, and other foreign matter that may collect on the contacts and piston, and viscosity changes in the oil.